1. Field of the Invention
The present invention relates to an image forming apparatus such as a photocopier, facsimile, printer, plotter, or a complex device having a plurality of these functions, as well as to a process cartridge for the image forming apparatus.
2. Description of the Related Art
To achieve high image quality using image forming apparatuses such as photocopiers, facsimiles, plotters, or complex apparatuses having these functions, a toner for use therein has been modified and developed in recent years, for example changing the shape of the toner from irregular ones to sphere ones, or downsizing the toner. Therefore, functions and performances required for a cleaning device for removing the residual toner are getting more and more difficult to achieve. One of the reasons for this is considered to be that the electrostatic force between the image-bearing member and the toner has been getting stronger. To prevent this problem, it is effective to apply a lubricity imparting agent to the image-bearing member. By applying the lubricity imparting agent to the image-bearing member, a film is formed on the image-bearing member and thus the electrostatic force is reduced, or the friction coefficient of the surface of the image-bearing member is decreased with respect to the toner, and thus the toner is easily removed, thereby improving the cleaning performance. This effect is enhanced as the circularity of the toner is increased, i.e. the toner becomes rounder.
When images of large image area with respect to a cleaning blade that is a toner removal member are inputted, or images of even small image area are continuously inputted in the same area, loads for cleaning become excessive for only the toner removal function of the cleaning blade. To solve this problem, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-330443 proposes, as a method which is not influenced by the toner amount of the input, to provide a uniformity unit which supplies a lubricant (lubricity imparting agent) after removing the toner by the cleaning blade, and then makes the applied lubricant uniform with respect to the photoconductor.
Meanwhile, for example, JP-A No. 08-234642 discloses a technology for control the applied amount of the lubricant depending on the image area.
However, it is difficult to control applied amount of the lubricant on the image-bearing member using the technology disclosed in JP-A No. 2000-330443, the lubricant is applied at a certain constant amount. In this case, there are problems such that the lubricant is consumed inefficiently, the supplied amount of the lubricant is not sufficient, and the like.
By using the technology disposed in JP-A No. 08-234642, the problem of large loads for cleaning is solved in the case where images of large image area are inputted with respect to the cleaning blade, as mentioned earlier. However, this technique does not solve the problem when images of a small image area are continuously inputted in the same area. Namely, in the case where a toner is continuously inputted in the same area even if a width of an image in a longer direction (an axial direction of the image-bearing member) is short, more amount of the toner is slipped out from the cleaning blade edge as the circularity of the toner is increased. As a result, the friction coefficient on the image-bearing member becomes large, and cleaning failures may occur.